<html>
<head>
    <meta charset="UTF-8">
    <title> Login </title>
    <style>
        html {
            width: 100%;
            height: 100%;
            overflow: hidden;
            font-style: sans-serif;
        }

        body {
            width: 100%;
            height: 100%;
            font-family: 'Open Sans', sans-serif;
            margin: 0;
            background-color: #4A374A;
        }

        #login {
            position: absolute;
            top: 50%;
            left: 50%;
            margin: -150px 0 0 -150px;
            width: 300px;
            height: 300px;
        }

        #login h1 {
            color: #fff;
            text-shadow: 0 0 10px;
            letter-spacing: 1px;
            text-align: center;
        }

        h1 {
            font-size: 2em;
            margin: 0.67em 0;
        }

        input {
            width: 278px;
            height: 30px;
            margin-bottom: 10px;
            outline: none;
            padding: 10px;
            font-size: 13px;
            color: #fff;
            text-shadow: 1px 1px 1px;
            border-top: 1px solid #312E3D;
            border-left: 1px solid #312E3D;
            border-right: 1px solid #312E3D;
            border-bottom: 1px solid #56536A;
            border-radius: 4px;
            background-color: #2D2D3F;
        }

        .but {
            width: 278px;
            min-height: 20px;
            display: block;
            background-color: #4a77d4;
            border: 1px solid #3762bc;
            color: #fff;
            padding: 9px 14px;
            font-size: 15px;
            line-height: normal;
            border-radius: 5px;
            margin: 0;
        }
    </style>
</head>

<body>
    <div id="login">
        <h1>HotDog</h1>
        <form method="post">
            <input type="text" required="required" placeholder="用户名" id="user"></input>
            <input type="text" required="required" placeholder="密码" id="pwd"></input>
            <button class="but" type="button" onclick='onSubmit()'>登录</button>
        </form>
    </div>
</body>

<script type="text/javascript">
    function onSubmit() {

        let username = document.getElementById("user").value;
        let password = document.getElementById("pwd").value;
        
        /**拼接参数 */
        let param = "?username="+ username
                    + "&password="+ password;
        
        let url =  "login_pt/judge" + param;

        /**原生ajax */
        var xhr = new XMLHttpRequest();
        xhr.open('GET',url,true);
        xhr.onreadystatechange = function(){
            if (xhr.readyState == 4 && xhr.status == 200 || xhr.status == 304) { 
                let result = xhr.responseText;

                if(result.indexOf('msg:') == '-1'){
                    window.location = result;
                }else{
                    alert(result.substr(4,result.length));
                }                  
            }
        }
        xhr.send();
    }

</script>

</html>